In conventional subsea pumps with a balance piston, the balance piston is placed at or near the pump outlet, or pump discharge. This solution is also described in textbooks as A. J. Stepanoff, “Centrifugal and Axial Flows Pumps, Design, and Application” 2nd Ed., Chapter 11.2 (1993); and J. F. Gulich “Centrifugal Pumps” 3rd Ed., Chapter 9.2.3 (2014). This location is favorable because for many pump applications there are greater variations in pressure at the pump discharge side than at the pump suction side. Indeed, for many applications the pump inlet pressure is relatively constant. A typical subsea application where this is the case is the injection of raw seawater, where the pump inlet pressure is relatively constant and is dictated by the ambient seawater pressure.
There have been some proposals to configure the balance piston in other ways. For example, in a subsea water injection system, in order to achieve enough discharge pressure, the system can consist of two water injection pumps operated in series. The second pump has a balance piston located in both ends. With such a solution, all seal chambers on both pumps are drained back to the suction (inlet) of the first pump. The barrier fluid pressure for both pumps is therefore regulated according to the first pump suction pressure. A disadvantage with this solution is that the balance piston on pump outlet for the second pump sees the total differential pressure for both pumps. This effectively limits the total differential pressure.